Gas detection apparatus



April 24, 1951 Filed May 19, 1948 Patented Apr. 24, 1951 `2,549,974 GAS DETECTION APPARATUS Charles W. Klug,

Chicago,

Ill., assignor to Stewart-Warner Corporation, Chicago, Ill., a corporation of Virginia Application May 19, 1948, serial No. 28,032

-The present invention relates to gas detection apparatus and particularly to apparatus for the detection of carbon monoxide in heated spaces, such as the heated interior of an airplane cabin.

This application is a continuation in part of my prior application Serial No. 481,425, filed April 1, 1943, now abandoned.

The primary object of the present invention is to provide a new improved gas detection apparatus wherein a controlled device, which may be a warning device, valve, or the like, is maintained in operated condition for a certain length of time upon the detection of the gas.

3 Claims. (Cl. 23u-255) A further object of the present invention is to providea new and improved gas detection apparatus wherein a controlled device is operated and maintained in operated position for a certain length oi time, and wherein an attempt is made to restore the detection apparatus to its initial d condition during the time the device is maintained in its operated state.

A further object of the present invention is to provide new and improved gas detection apparatus of the character wherein a gas sensitive substance is normally supplied with a medium in which the presence of gas is to be detected and, wherein upon detection of the gas, a gas counteracting the eiects of the first gas is supplied at least a predetermined length of time to counteract the effects of the gas to be detected.

Other objects and advantages of the present invention will become apparent from the ensuing description, in the course of which reference is had to the accompanying drawings, in which:

Fig. l is a diagrammatic representation of one V embodiment of the invention; and

Fig. 2 is a similar representation of a second embodiment of the invention.

The apparatus of the present invention utilizes a substance having a photocharacteristic that varies in response to the presence of the gas to be detected. More particularly, the photo characteristic is the light transmitting characteristic and the gas to be detected is carbon monoxide. It is well-known that carbon monoxide .is a Very deadly gas and that its presence in a space occupied by people should be immediately detected, particularly when the space is the heated interior of an airplane into which carbon monoxide may be injected along with heated air. Under usual conditions the heated air supplied to the interior of the cabin would not contain any carbon monoxide, but should the heat exchanger be, for instance, of the exhaust gas type, and should it be punctured as by a bullet, then the carbon monoxide present in the exhaust gases enters the interior of the cabin.

In the copending application of Willard H. Farr, William F. Fagen and Frank A. Fanta, Jr., application Serial No. 479,710, iiled March 19, 1943, and in my copending application Serial No. 481,426, iiled April 1, 1943, both now abandoned, there are disclosed methods of and apparatus for detecting the presence of toxic gases, especially carbon monoxide. The apparatus utilizes a substance' sensitive to the presence of carbon monoxide known as the National Bureau of Standards Colcrimetric Carbon Monoxide indicating Gel. The chemical description and method of making this gel are fully disclosed in an article under the title of Rapid Determination of Small Amounts of Carbon Monoxide (Preliminary Re'- port on the NBS Colorimetric Indicating Gel) by Martin Shepherd. This article appeared in Industrial and Engineering Chemistry (Analytical Chemistry), volume 19, page 77, February 1947. Thisl gel is yellow in color until exposed to carbon '.,ioncxide when its color changes from yellow progressively toward a dark blue-green. Thus, in the event there is carbon monoxide present in the air to be tested, the substance changes from a yellow to a darli blue-green color. The apparatus also includes a light source and a photosensitive device upon which impinges light passing through the sensitive substance to change the conductivity of the device. This change in conductivity of the photosensitive device is utilized to control the conductivity of an electron tube controlling a relay, which in turn controls either a signal or some suitable device controlling the operation of the heater, or of a valve controlling the supply of heated air to the interior of the cabin.

. The sensitive substance may be returned from its darla blue-green color to its initial yellow color, and from a nonsensitive tok its initial sensitive condition by the restorative action of another gas.r Ozone is one of the gases and the oxides oi nitrogen are other gases having this restorative eiiect, all as disclosed and claimed in the two aforementioned applications.

The present invention relates to apparatus of the character described above, and more particularly to the arrangements for controlling the restoring or counteracting operations. f

Referring now to Fig. 1, the sensitive substance, indicated by the reference character I0, is located within the central portion of a transparent glass tube l2 so that light from a lamp I4 passes through itand impinges upon a photosensitive device, such as the photoelectric cell I6. The photoelectric cell controls the conductivity of an electron tube I8, which has a control relay 20 connected in its plate or anode circuit and which relay is normally in its operated position, as indicated.

The sensitive substance, hereafter to be referred to as the carbon monoxide indicating gel, has at its opposite ends some silica gel 22, while the ends of the tube are filled with some flow restricting material, such as glass Wool 24, which also serves to keep the indicating and silica gel in place.

Under normal conditions of operation, air from within the heated cabin of an airplane or the heated `air to be supplied to the airplane is passed slowly through the tube I2. The air to be tested flows through a conduit 26 having a normally open passageway 28 controllable by a two-position valve 38, movably mounted within a tting V3 I, and a conduit a2.

yor it may be apparatus for producing ozone or the oxides of nitrogen. Its outlet end is connectedby conduit -36 to the iitting 3i. In the indicated positionof valve 30, the conduit 36 is closed to prevent passage of the restoring gas through the tube 32 and the tube I2, while conduit 26 is open totube 32. When, however, the valve 30 is moved, aswill be described hereinafter, the restoring gas flows through the passagewayr38 and thence Vthrough the tube 32 to the indicating gel-containing tube I2.

The means forY supplying the restoring gas is rendered eiectiveY to supply the gas when the concentration of carbon monoxide reaches some predetermined value. At this time electric energy is supplied to the apparatus 34 through the conductors 4I) and 42. At the same time, the valve 30 is shifted by the energization of a solenoid 44 which is supplied with energy through conductors 4B and 48 and moves valve 38 through an apertured armature 49 secured to the valve and slidable in conduit 25. When energized, the solenoid moves valve 3e to the right, as viewed in Fig. l, against a suitable biasing means, such as a spring 50.

The energization of the gas supplying means 34 and solenoid 44 is under the control of a photoelectric cell I6, and the tube I8 and the'relay 20 associated therewith. The photoelectric cell is connected across a4 pair of -power supply conductors 52 and 54 through a resistor 56 connected to the negative power supply line 54 and to the cathode o the photoelectric cell. The light I4 is -connected directly across the power supply lines by the conductors 58 and 60.

The electron tube I8 controlled by the photoelectric cell is preferably arranged to be conductive under normal conditions, i. e., when the concentration of carbon monoxide is below a pre- 1 tion of the resistor 53 and cathode of the photoelectric cell so that it becomes more negative as less light impinges upon the cell. As the grid swings more negative, less current ilows through the tube until at some value of current ow, the relay 20 is released. The relay is connected across the anode 64 of the tube and the positive powerY supply line 52 by the conductors 66 and 68.

The grid bias is supplied by a bias resistor I0 adjustably connected through a connection I2 to the cathode 'I4 of the tube. To provide the desired normal grid bias, the bias resistor 'I0 is connected to theY positive power supply line through `a bleeder resistor 16. er I8 is connected directly across the power supply lines.

The relay 20, which is normally in its operated position, controls the position of a switch connectedV by conductor 82 to the positive powerV supply line. The circuit controlled by the switch is normally open, but when the relay is released, the switch 85' completes a circuit across conductor 82 and a conductor 84 leading to the previously mentioned restoring gas supplying means 34 and valve operating solenoid 44. Thus, Vwhen the switch is closed, in response to the presence of a predetermined concentration of carbon monoxide, the flow of air through the indicating gel tube is stopped by movement of valve 30 and the tube is supplied with restoring gas from apparatus 34 until the energizing circuit is opened.

At the same time that the restoring means is rendered effective, a controlled device 85 is operated. This device may be a warning signal or a heat exchanger operation controlling de- Y vice, or a valve controlling the supply of heated air to the interior of the cabin. The energizing circuit for this device includes the conductor 82, switch 85, conductor 84 and a conductor 88 connected to the negative power supplyline 54.

. Once the restoring gas supplying means, the solenoid 44 and the control device have been operated, they are maintained in their operated conditions-for at least a certain time interval by a relay, indicated generally by the reference character 98. This relay includes a relay winding 92 energized by the closure of switch 88. Its energizing circuit includes conductor 82, switch 80, a conductor 94 leading to one terminal of the winding, and a conductor 96 leading from the other terminal of the winding to power supply line 54. When the relay is energized, it closes .a switch 98 preferably made of bimetallic material and which, once operated, is maintained in its operated position by some suitable means, such as a permanent magnet I 00. The switch 98 'is in parallel with switch 8l! and is arranged periodically to be opened by a heater I|l2 located in proximity thereto. The switch is connected across conductors 52 and 84 by conductors |84 and IDB. Heater I02 is connected across conductors IDB and 54.

In operation the power supply lines 52 and Vi4 are connected to some suitable source of direct current, which may be the usual 24 volt source found in the airplane. When the indicating gel is in its initial condition, the light passing therethrough from the lamp I4 to the photoelectric cell It *renders the grid S2 of tube I8 positive to an extent sufficient to maintain relay 2G in its operated position with the result switch 82 is opened and the various devices controlled by that switch are tie-energized. These devices include the restoring gas supplying means Zul, the solenoid 44, controlled device 8e and the relay 92. Under these normal conditions, the liimetallic s-witch @8 is also open.

Air from within the interior of the cabin passes The cathode heatthrough conduit 25 and passage 28 and conduit 32 to the indicating gel tube I2. As long as no carbon monoxideis present in the air to be tested, the indicating gel maintains its initial color. Should there' be slight amounts of carbon monoxide present sufcient over a period of time to change the color of the indicating gel, or should there be a considerable concentration of carbon monoxide present, thereby to change the color of the gel, the grid of the electron tube I8 is rendered more negative to decrease the current ilow through the tube. At a predetermined concentration, determined by the adjustment of gridibias control l2, the relay 2li is released and the switch 6D closed. The closure of the switch immediately operates the controlled device 86, places vthe restoring gas supplying means 34 into operation, and connects its output to the indicating gel tube and at the same time cuts oi the further supply of air from withv in the intrior of the cabin to the tube. Simultaneously the relay 92 is energized and operates switch member 98 to its circuit closing position wherein it is held bythe magnet IEB for at least a certain length of time, depending upon the effect of the heater lez which heats the switch to open it. y

Should the change in color of the indicating gel have resulted from a cumulative eiect of slight concentrations oi carbon monoxide, then the indicating gel will be cleared by the first operation of the apparatus. Upon clearance, the relay 2B is again energized suiiiciently to open switch 89. However, the opening of the switch does not Cle-energize the various apparatus for the reason that the switch 9S is in parallel with switch 3B and it is maintained closed by magnet E66. However, the heater m2, which is connected across the power lines through switch 93, finally effects the opening of switch 98 with the result that the apparatus as a whole is re turned to its initial condition.

Should the concentration of carbon monoxide be of a higher predetermined or toxic value, then the restoring means is not effective to reu store the indicating gel to its initial condition even though continuously operated. The result is that relay 29 remains in its released position and switch 80 closed. During the continued operation of the restoring means, the switch 98 is periodically7 opened by the action of the heater, but such periodic opening has no effecton the operation of the apparatus since the switch 80 remains closed.

However, when the indicating gel has been cleared, as a result of the repair of the heater, or because of the passage of the airplane from a 'region wherein considerable carbon monoxide might be present, the relay 2G is again operated to open switch 8i), after which the bimetallic switch 98 opens the energized circuit for the device 85, the solenoid 44 and the restoring means 34. The apparatus is thus returned to its initial condition ready for further detection operations.

The apparatus illustrated in Fig. 2 corresponds for the most part with the apparatus illustrated in Fig. l, and like parts have been indicated by like reference characters. The primary distinction between the two embodiments resides in the arrangement of the second in such manner that the restoring means 34 and solenoid 54 are controlled by the relay 2G, whereas the controlled device 86 alone is controlled by the relay 32.

The controls are so arranged that upon a predetermined change in color of the indicating gel the relay 2i) is energized toV place the restoring means in operation and to operate the valve 50. At the saine time relay 2i) energizesf'relay 92, and "the latter effects operation of the' ccnl trolled device 86. In this arrangement, therestoring means is arranged to be effective to clear the indicating gel in a short period, such as about thirty seconds, even in the presence oftoxic concentrations'or" carbon monoxide. Upon such clearance the relay 2l) is released to render inef` fective the restoring means and to de-energize relay 92. The controlled device Sii, however, is not released as it is maintained'in its operated condition by the bimetallic switch element 9 8, which is held in its closed position by magnet HJG, and 'which is heated by the heater IGZ until opened.' Switch 95 is thus maintained in its closed position for a length of time after the deenergization of relay t2 upon subsequent `op'-J eration of relay 2l).

Referring now more particularly to Fig. 2, it may be noted that relay 2G is normally oper# ated and switch 8G is open. When closed, switch 8G connects conductors 82 and Sii to 'complete energizing circuits for solenoid fifi and the restoring means 34 through conductors 32 and 84. Upon closure switch also completes an ener'- gizing circuit for 'relay 92 through conductors 94 and 96. Relay 92 is effective when operated to close the bimetallic switch element Se, thereby to complete a circuit across conductors HM and U06, the latter of which is connected to one terminal of the controlled device Sii, the other terminal of which is connected by conductor 88 to the negative power supply line 54. When the switch is closed by release of relay 26, the heater |92 is also energized as it is connected in parallel with device 86. The birnetallic switch element is so arranged that the heat from heater |92 tends to open against the force exerted thereon by magnet I @2, with the result that switch opens a certain time interval after de-energization of relay 92 but remains closed aslong as relay 92 is energized.

The apparatus is placed in4 operation in the same manner as that of the embodiment of Fig. 1, and under normal conditions the relay 2&1 is in its operated position while relay 92 is released'.

When the air flowing from within the interior of the cabin through and in contact with the in`- dicating gel contains' carbon monoxide, the indicating gel I0 is discolored and the electron tube I8 is rendered less conductive until at a predetermined current Value relay 2S is released, Switch 3i] is thereupon closed to place the restorL ing means in operation and to operate the Valve Si). At the same time, relay 92 is energized to close bimetallic switch 98 and the heater |02 is also energized to provide heat tending to open switch 98.

The restoring means is effective shortly to restore the indicating gel to its initial condition. If the discoloration of the indicating gel resulted from a cumulative eiTect of slight concentrations of carbon monoxide over a period of time, then the relay 26 is operated and remains in its operated position so that, when switch 98 is opened by the application of heat, the apparatus is returned to its initial condition. If, on the other hand, the change in color resulted from a predetermined concentration of carbon monoxide, then the indicating gel would be restored to its original condition only temporarily, with the result that relay 2G would be operated and then released piror to the opening of switch 98., so that relay 92 would again be operated. It may be seen, therefore, that in this embodiment, the Vcontrolled -device remains in its operated condition if carbon monoxide is present in a predetermined concentration, and the restoring means is periodically rendered effective to test the condition of the airsupplied to the interior of the cabin'.`

From the foregoing detailed description of the present invention, it may be noted that it may be embodied in various forms and that while the invention is directed .more particularly to the detection of the presence of carbon monoxide, its principles ,may be applied to the detection of other gases.

It will thus be apparent to those skilled in the -art that numerous modifications and variations may be made without departing from the underlying principles of the invention` I therefore desire, by the following claims, to include within thescope of the invention all such modifications and variations by which substantially the results thereof .may be obtained by substantially the .same or equivalent means.

.I claim:

11. An apparatus for detecting the presence of a gas constituent in a medium by the use of a substance in gas permeable form, which under.-

.goes a photocharacteristic Vchange in the pres-l ence of s aid gas, said apparatus comprising: a light transmitting container constructed to supportsaid .substance for passage of gas therethrough, a conduit kconnected to said container having two openings at one endV thereof, a tube for conducting the medium to be tested to the container connected to one of said openings, said tube including a valve, a source of restoring gas including an outlet tube connected to the other of .said openings, said valve so arranged that when in a first position it closes the opening con `nected to the source vof restoring gas and when .in a second position it closes the opening connected to the tube for conducting the medium te be tested, a lamp and a photoelectric cell arranged to receive light from the lamp through the container, and .electrical valve shifting means operated by said photoelectric cell to shift said valve.

2. An apparatus for detecting the presence o1 .I

a gas .constituent in a medium by the use of a substance in gas permeable -form, which undergoes a photocharacteristic change in the presence of said gas, said apparatus comprising: a light transmitting container constructed to support said substance for passage .of gas therethrough, aconduit connected to said container having two .openings at one end thereof, a tube for ,conducting the medium to be tested to the container connected to one of said openings, a source .of restoring gas including an outlet tube connected to the other of saidopenings, a valve so arranged that When in a first position it closes the opening connected to the source of restoring gas and when in a second position it closes the opening connected to the tube for conducting the medium to be tested, a lamp and a photcelectric cell arranged to receive light from the lamp through the container, and electrical valve shifting means operated by said photoelectric cell to shift said valve. i

3. An apparatus for detecting the presence or -g-'as constituent in a medium by the use of a substance in gas permeable form, which undergoes a photocharacteristic change in the presence of said .-gas, said apparatus comprising: a light transmitting container constructed to support said substance for passage of gas therethrough, al conduit connected to said container having two openings at one end thereof, a tube for conducting the medium to be tested to the container connected to one of said openings-a sourcey yof restoring gas including an outlet tube connected to the other of said openings, a valve so arranged that when in a first position it closes the opening connected to the source of restoring gas and /when in a second position it closes the opening connected to the tube for conducting the medium to -be tested, a lamp and a photoelectric cell arranged to receive light from the lamp through Ythe container, and electrical valve shifting means operated by said photoelectric cell to shift said valve from the rst rposition to the second posi? tion when the intensity of the light received by said cell reaches a predetermined value, and timingvmeans for shifting said valve from said second position to said first position after the expiration ofA a predetermined time interval.

CHARLES W. KLUG.

REFERENCES CITED The following references lare of record in the file of this patent:

UNITED STATES PATENTS Number Name `Date .1,707,624 Brown Apr. 2, 1929 1,969,626 Simon et al.V Aug. 7, 1934 2,019,871 Pettingill et al Nov. 5, 1935 2,295,366 Stout Sept. 8, 1942 2,349,963' Harrison May 30, 19,44

FOREIGN PATENTS Number Country Date 405,887 Germany Nov. 11, 1924 

2. AN APPARATUS FOR DETECTING THE PRESENCE OF A GAS CONSTITUENT IN A MEDIUM BY THE USE OF A SUBSTANCE IN GAS PERMEABLE FORM, WHICH UNDERGOES A PHOTOCHARACTERISTIC CHANGE IN THE PRESENCE OF SAID GAS, SAID APPARATUS COMPRISING: A LIGHT TRANSMITTING CONTAINER CONSTRUCTED TO SUPPORT SAID SUBSTANCE FOR PASSAGE OF GAS THERETHROUGH, A CONDUIT CONNECTED TO SAID CONTAINER HAVING TWO OPENINGS AT ONE END THEREOF, A TUBE FOR CONDUCTING THE MEDIUM TO BE TESTED TO THE CONTAINER CONNECTED TO ONE OF SAID OPENINGS, A SOURCE OF RESTORING GAS INCLUDING AN OUTLET TUBE CONNECTED TO THE OTHER OF SAID OPENINGS, A VALVE SO ARRANGED THAT WHEN IN A FIRST POSITION IT CLOSES THE OPENING CONNECTED TO THE SOURCE OF RESTORING GAS AND WHEN IN A SECOND POSITION IT CLOSES THE OPENING CONNECTED TO THE TUBE FOR CONDUCTING THE MEDIUM TO BE TESTED, A LAMP AND A PHOTOELECTRIC CELL ARRANGED TO RECEIVE LIGHT FROM THE LAMP THROUGH THE CONTAINER, AND ELECTRICAL VALVE SHIFTING MEANS OPERATED BY SAID PHOTOELECTRIC CELL TO SHIFT SAID VALVE. 